A steam generator for a pressurized-water nuclear reactor, comprises a cylindrical upstanding housing having a steam output outlet at its top and provided with a feed-water inlet, the bottom of the housing being closed by a horizontal tube sheet of cylindrical contour. An upstanding, inverted U-shaped heat exchanger tube bundle has its inlet and outlet legs, each comprising a multiplicity of tubes and defining a generally semicylindrical cross-sectional contour, mounted in holes formed in the tube sheet. A hemispherical enclosure below the tube sheet has a vertical partition separating it into inlet and outlet manifolds, respectively provided with inlet and outlet water-coolant connections, defines inlet and outlet chambers for the holes opening through the tube sheet and in which the heat exchanger legs are mounted. Within each of these chambers the cross-sectional contour adjacent to the tube sheet is of a generally semi-circular contour and cross section.
In operation, water coolant from the pressurized-water reactor is circulated through the heat exchanger via the inlet and outlet manifold chambers. The water coolant picks up radiation activity from the reactor and transfers it to these chambers and with time these chambers become active to a degree which is dangerous to a workman who might enter either chamber when empty, and remain there far too long a time.
Using either of the chambers as an example, it is provided with a manhole which, when opened, permits a workman to enter the chamber, the latter being empty and the reactor normally being in a shut-down condition during such time. A workman must enter this chamber whenever the heat exchanger tubes are to be internally inspected or repaired because such work must be done via the bottom ends of the tubes and their holes through the tube sheet.
It is possible to make such inspection and repair by the workman entering the chamber, by attaching the end of a flexible guide conduit to the tube sheet at the hole of the tube to be inspected or repaired. After such attachment, the workman may leave the chamber and from a safer location a flexible carrier hose can be inserted via this guide conduit into the heat exchanger tube. The carrier hose may carry on its inserted end various devices for either inspection or repair, as by plugging the tube involved. This procedure must be repeated as to each of the heat exchanger tubes, thus subjecting the workman to an undesirably prolonged exposure to the radiation activity persisting within the chamber.
It is apparent that the foregoing presents a problem requiring a solution.